Separation and purification of nanoparticles (NPs) or biomolecules become increasingly important both for fundamental studies and applications. Known separation techniques include size exclusion chromatography, size-selective precipitation, gel electrophoresis and (ultra) centrifugation. Although these techniques can be used to separate according to size they are usually time- or energy consuming. An emerging alternative to these methods is represented by filtration techniques. In particular, ultrafiltration is a pressure-driven separation process in which porous membranes retain particles larger than the membrane cut-off (ranging from 2 to 100 nm). Membrane processes allow fast separation, the use of small solvent volumes, and are suitable for separation and purification of various NPs. Filtration can be easily scaled up, allowing separation and purification on the industrial scale. All commercially available filtration membranes used today are either polymer-based or ceramic. Supramolecular structures have been used as templates for porous membranes and for modification of membrane pores. The challenge in creating supramolecular filtration membranes relates to the robustness and the structure that is adequate for filtration, requiring a uniform porous array that maintains its integrity and pore sizes under the forces created by percolation of solvents and solutes during the filtration process.
Membrane filtration is an essential tool in the biotechnological industry and appears to be particularly useful for the purification and concentration of proteins. Moreover, membranes can be used for immobilization and biocatalytic utilization of enzymes. As enzymes catalyze reactions under very mild conditions, exhibiting efficiency and selectivity largely unmatched by synthetic catalysts, such membrane reactors are emerging components in new, environmentally friendly industrial processes (heterogeneous biocatalysis), which may supplement or replace traditional chemical methods.
Separation of chiral compounds is of great interest since the majority of bioorganic compounds (sugars, amino-acids, sugar, proteins, nucleic acids) are chiral. Chirality is a major concern also in the pharmaceutical industry, since drugs with different chirality may have different pharmacological activities as well different pharmacokinetic and pharmacodynamic effects. Chiral HPLC and chiral GC have proven to be one of the methods for the direct separation of enantiomers. However, there is still no one universal column that has the ability to separate all classes of racemic compounds.
Filtration membranes which are used today are based on polymers or ceramics. Supramolecular systems have been utilized as templates for polymer membrane pores, rather than the membrane material itself. Recently, substantial progress has been made in fabricating supramolecular membranes. However, these membranes employ conventional high molecular weight polymers, and those that were applied to biological systems underwent elaborate modifications of the self-assembled material prior to use.